Diagnosis devices already exist that are “exported” to a patient's home, i.e. away from care centers. Such devices need to be simple to use, and the self-taken sample needs to be measured on site or stabilized so as to be stored for several days in order to enable it to be sent (by post) to a care center for measurement purposes.
That procedure is increasing because it avoids the need for patients to travel and it enables a greater number of tests to be performed, which tests are often non-invasive and almost non-traumatic. One of the best examples is glucose testing for diabetes, which is managed completely by the patient on the basis of 1 microliter (μL) of blood.
The invention relates more particularly, but not exclusively, to a device for taking blood in order to determine the protein composition of a blood sample, in particular in the context of epidemiological studies or searching for biomarkers.
For this purpose, the blood needs to be fractioned into a plasma phase containing the proteins and a cell phase. In this application, the cells, and mainly red corpuscles, must be excluded but without being lysed in order to avoid disturbing measurement of the protein spectrum as performed using a mass spectrometer.
It is not possible to incorporate a spectrometer in a discardable device, so when the patient is not present close to the spectrometer it is necessary to stabilize the plasma for the time it takes to be transported to the measurement center, which time is generally several days. For this purpose, the plasma is preferably absorbed and dried on a specific medium.
In general, nearly all fragmentation techniques, whether for transfusion purposes, or for analysis purposes, rely on the principle of centrifuging blood. Blood cells present density that is slightly greater than that of plasma and can therefore be separated easily and effectively using conventional centrifuging techniques.
Nevertheless, that technique requires dedicated equipment and qualified personnel in order to take the blood sample and treat it. Premises for taking samples and for analyzing them are often far apart and samples often wait for many hours before they can be analyzed. During this latency time, the constituent elements of the blood (including its proteins) degrade progressively.
Furthermore, present sample-taking and fragmentation techniques are designed for treating several hundred milliliters (mL), whereas most tests require only a few hundred μL. Extracting several mL of blood is traumatic for some patients, and must not be repeated too often.
Various prior art devices exist that are suitable for separating blood cells using sample volumes that are limited to a few hundreds of microliters of blood.
In such devices, separation is performed by filters made of fiber materials, namely glass fibers, as described in U.S. Pat. No. 5,364,533 (Sanwa Kagaku Kewkyusho) for collecting a volume of blood equal to about 1 milliliter, or as described in patent application EP-0-633 808 (Gostechnology) where the glass fibers are in the compressed state.
It is also known to make use of a clumping agent or an agglutinizing agent as a separating agent. This is described as being optional in above-mentioned U.S. Pat. No. 5,364,533 and essential in U.S. Pat. No. 5,558,834 (Bayer Corp.) and U.S. Pat. No. 6,106,732 (Binax Services).
Those techniques present the following drawbacks.
Firstly, agglutinizing agents present varying selectively depending on protein type, thereby creating bias in terms of the representativity of the sample treated in that way.
Furthermore, fibers, and in particular glass fibers, do not retain all corpuscles, thereby disturbing mass spectrometer measurement in which it is important to use plasma that is very clear, i.e. without any hemoglobin from red corpuscles.